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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

PRODUCTION OF HIGH-TEMPERATURE PLASMAS DURING THE EARLY PHASES OF A C9.7 FLARE

Explosive chromospheric evaporation is predicted from some current solar flare models. In this paper, we analyze a flare with high time cadence raster scans with the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft. This observation covers an area of 240'' x 240'', with the 1'' slit in about 160 s. The early phases of a C9.7 flare that occurred on 2007 June 6 were well observed. The purpose of our analysis is to study for the first time the spatially resolved spectra of high-temperature plasma, especially from Fe XXIII and Fe XXIV, allowing us to explore the explosive chromospheric evaporation scenario further. Sections of raster images obtained between 17:20:09 and 17:20:29 (UT) show a few bright patches of emission from Fe XXIII/Fe XXIV lines at the footpoints of the flaring loops; these footpoints were not clearly seen in the images taken earlier, between 17:17:30 and 17:17:49 (UT). Fe XXIII spectra at these footpoints show dominating blueshifted components of -(300 to 400) km s{sup -1}, while Fe XV/XIV lines are nearly stationary; Fe XII lines and/or lower temperature lines show slightly redshifted features, and Fe VIII and Si VII to He II lines show {approx}+50 km s{sup -1} redshifted components. The density of the 1.5-2 MK plasma at these footpoints is estimated to be 3 x 10{sup 10} cm{sup -3} by the Fe XIII/XIV line pairs around the maximum of the flare. High-temperature loops connecting the footpoints appear in the Fe XXIII/XXIV images taken over 17:22:49-17:23:08 (UT) which is near the flare peak. Line profiles of these high-temperature lines at this flare peak time show only slowly moving components. The concurrent cooler Fe XVII line at 254.8 A is relatively weak, indicating the predominance of high-temperature plasma (>10{sup 7} K) in these loops. The characteristics observed during the early phases of this flare are consistent with the scenario of explosive chromospheric evaporation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Collisional transport coefficients of dense high-temperature plasmas within the quantum Landau-Fokker-Planck framework

In this paper, we extend the long-established formulas for the transport coefficients of classical plasmas inside the dense plasma regime for temperatures and densities where the classical Landau equation breaks down but its quantum extension that includes quantum degeneracy effects is valid. To this end, the quantum Landau kinetic equation is solved by the Chapman-Enskog method. The mathematical derivation is done in full generality, i.e., for multicomponent systems and to all orders of the polynomials expansion used to approximate the distribution functions. We apply the general results to two important examples, the electron gas model and an electron-ion plasma model consisting of one type of ions of any charge. We discuss the combined effects of the Pauli exclusion principle, of the electron-electron, and of the electron-ion collisions on the transport coefficients and on the convergence of the Chapman-Enskog method. For the electron gas model, the effect of the Pauli exclusion principle on the transport coefficients rapidly becomes non-negligible outside the domain of validity of the classical Landau equation. For the electron-ion plasmas, the effect of the Pauli exclusion principle depends sensitively on the ion charge Z and varies non-monotonically with Θ. For instance, for ion charge Z = 1, the electrical conductivity is increased by up to ~30% compared to its classical value over the range of degeneracy parameters studied, the thermal conductivity is reduced by up to ~9%, and the shear viscosity coefficient is increased by up to ~13%. Finally, in the Lorentz gas ( Z → ∞ ) limit, the electrical conductivity is reduced by up to ~14% compared to its classical value over the range of degeneracy parameters studied, the thermal conductivity is reduced by up to ~39%, and the shear viscosity coefficient is not affected.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1980

Thermal bremsstrahlung from high-temperature plasmas

Analytic expressions are derived for the total bremsstrahlung energy-loss rate per unit volume and the spectral emission rate of a very hot (10 million K to 1 billion K) plasma. At these temperatures the principal contribution to emission can be computed from the nonrelativistic limit of electron-ion bremsstrahlung in the Born approximation. Modifications to this rate are evaluated from (1) relativistic corrections to the thermal-electron velocity distribution function, (2) relativistic and spin corrections to the nonrelativistic electron-ion bremsstrahlung cross section, (3) electron-electron bremsstrahlung, and (4) first-order Born approximation corrections to electron-ion bremsstrahlung.

Gould, R. J.↗
DOE OSTI2013

Simultaneous measurement of nitrogen and hydrogen dissociation from vacuum ultraviolet self-absorption spectroscopy in a developing low temperature plasma at atmospheric pressure

We demonstrate a method for determining the dissociation density of N and H atoms present in a developing low temperature plasma, based on the emission and self-absorption of vacuum ultraviolet radiation produced from the plasma. Spark plasmas are produced via pulsed discharge in N{sub 2}/H{sub 2} mixtures at atmospheric pressure, where information on the dissociated densities of the constituent gas molecules is desired without employing invasive diagnostic techniques. By analyzing the self-absorption line profile of 121.5 nm Lyman-{alpha} H radiation emitted within the first {approx}1.0 mm of plasma near the anode tip, a peak dissociated H atom concentration of 5.6 Multiplication-Sign 10{sup 17} cm{sup -3} was observed {approx}100 ns into spark formation, with an estimated electron density of 2.65 Multiplication-Sign 10{sup 18} cm{sup -3} determined from Stark broadening. Similarly, simultaneous line fitting of the N 120.0/124.3 nm emission profiles revealed a peak dissociated N atom concentration of 3.8 Multiplication-Sign 10{sup 17} cm{sup -3} during the same discharge period.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Electron kinetics in low-temperature plasmas

This work presents an overview of recent advances in the field of electron kinetics in low-temperature plasmas (LTPs). It also provides author's views on where the field is headed and suggests promising strategies for further development. The authors have selected several problems to illustrate multidisciplinary nature of the subject (space and laboratory plasma, collisionless and collisional plasmas, and low-pressure and high-pressure discharges) and to illustrate how cross-disciplinary research efforts could enable further progress. Nonlocal electron kinetics and nonlocal electrodynamics in low-pressure rf plasmas resemble collisionless effects in space plasma and hot plasma effects in fusion science, terahertz technology, and plasmonics. The formation of electron groups in dc and rf discharges has much in common with three groups of electrons (core, strahl, and halo) in solar wind. Runaway electrons in LTPs are responsible for a wide range of physical phenomena from nano- and picoscale breakdown of dielectrics to lightning initiation. Understanding electron kinetics of LTPs could promote scientific advances in a number of topics in plasma physics and accelerate modern plasma technologies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Advancing the Predictive Understanding of Low Temperature Plasmas

The purpose of this paper is to characterize the need for improved predictive capabilities in low-temperature plasma (LTP) science, and to identify possible means of accomplishing this. While these means may constitute an initiative of their own, we consider these ideas to have widespread importance to discovery plasma science. Therefore, it is our hope that these ideas are more generally incorporated in future work.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Low-Temperature Plasma Treatment for Enhanced Recovery of Highly Valued Critical REEs from Coal (Final Technical Report)

The principle objective of this project was to develop a novel process flowsheet using low-temperature plasma treatment (LTP) integrated with conventional hydrometallurgical processes to recover rare earth elements (REEs), especially highly valued REEs (i.e. scandium and critical REEs), from coal and coal byproducts. LTP treatment was used to pretreat the solid feed material prior to leaching in an effort to improve the leaching characteristics of the REEs and potentially reduce acid consumption. Initially, a detailed experimental program was performed on a laboratory LTP furnace to identify a set of process parameter values to be used for assessing the enhanced leaching performance achieved on four specific gravity fractions of West Kentucky No. 13 and Fire Clay coarse coal refuse materials. High-temperature oxidation (HTO)) was also evaluated as a means for improving REE leachability on the same fractions of both coal sources. The lixiviants used to assess leachability improvements included i) untreated water, ii) 0.1 M ammonium sulfate solution and iii) 1.2 M sulfuric acid solution at a temperature of 75°C. The laboratory data was used to develop multiple process flow sheets using HTO only to produce a rare earth oxide mix concentrate or utilizing both LTP and HTO treatment processes to generate a high purity heavy REO mix concentrate and a light REO mix concentrate. A techno-economic analysis was performed on each circuit.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2012

Silanization of Low-Temperature-Plasma Synthesized Silicon Quantum Dots for Production of a Tunable, Stable, Colloidal Solution

We present a method for grafting silanes onto low-temperature-plasma synthesized silicon quantum dots. The resulting solution of dots is characterized with Fourier transform infrared spectroscopy and transmission electron microscopy, and determined to be a colloidal suspension. The silane is attached at a single point on the quantum dot surface to avoid cross-linking and multilayer formation, and photoluminescence spectroscopy shows the colloidal suspension of dots is stable for over two months in air. The hydroxyl-terminated surfaces required for silanization are created by wet chemical etch, which can be used to tune the luminescence of the silicon dots in the green- to red-wavelength range. We find, however, that the wet etch cannot move the emission into the blue-wavelength range and discuss this observation in terms of the nature of etching process and origin of the emission. In addition, we discuss the photoluminescence quantum yield in the context of other passivation and synthetic techniques.

14 SOLAR ENERGY↗
NASA NTRS1990

Low-temperature plasma technology as part of a closed-loop resource management system

The results of this testing indicate that the agitated low-temperature plasma reactor system successfully converted carbon, hydrogen, and nitrogen into gaseous products at residence times that were about ten times shorter than those achieved by stationary processing. The inorganic matrix present was virtually unchanged by the processing technique. It was concluded that this processing technique is feasible for use as part of a close-looped processing resource management system.

Hetland, Melanie D.↗
DOE OSTI2023

Brewster angle-cavity ringdown spectroscopy for low temperature plasma measurements in multiphases

Here we report on the development of a Brewster angle-cavity ringdown spectroscopy (BA-CRDS) system for low temperature plasma diagnostics. The system can measure gas species in solutions, with a detection limit (minimum detectable absorbance) of 9.1 × 10 -5 , which is equivalent to a detection limit of 0.04 parts per billion for measuring OH radicals in water at 308 nm. With higher reflectivity ringdown mirrors and improved design of a Brewster angle cell, the detection limit can potentially be up to 10 -6 or lower. In this exploratory study, the absorption cross sections of HgBr 2 and H 2 O 2 in the aqueous phase at 256 nm are measured to be (1.8 ± 0.1) × 10 -18 cm 2 and (5.2 ± 0.5) × 10 -20 cm 2 , respectively. Furthermore, temporal profiles of absorbance from distilled water, HgBr 2 , and H 2 O 2 solutions when interacting with a helium atmospheric plasma jet are individually characterized at different plasma powers, gas flow rates, and/or solute concentrations. The observed linear temporal profiles of absorbance from the plasma-interacted water suggest formation of H 2 O 2 from plasma-generated OH radicals, while the nonlinear temporal profiles from the plasma-treated HgBr 2 solutions reveal possible removal of HgBr 2 by OH radicals. Our results demonstrate that the new BA-CRDS system is a powerful tool for quantification of reactive plasma species in multiphases or other complex settings.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Final Technical Report - Rapid Surface Microanalysis using a Low Temperature Plasma

This project focused on improving our current understanding and scientific knowledge in the area of plasma-surface interactions and plasma assisted material synthesis related to advanced microelectronics and nanotechnology. Current challenges include: controlling the interaction of Low Temperature Plasma (LTP) with a single layer of atoms to manufacture integrated circuits, continued miniaturization of integrated circuits, LTP processing of material surfaces and thin films to enable industrial scale fabrication of advanced microelectronics, synthesis of new materials, nanomaterials, nanotubes, and complex materials, Technology developed in this subtopic is of value to either (i) enable scans of surfaces (~1 sq. cm area) using various microscopies (electron, optical, other) at high resolution (micron or sub-micron resolution) rapidly (hours or days rather than years to complete a high-resolution scan of such a large surface area), or (ii) enable scans of surfaces (~1 sq. cm area) using various microscopies (electron, optical, other) at relatively low resolution rapidly, then apply algorithms to select spots for micron-scale imaging. Sputtering occurs when particles of a solid material are ejected from its surface by energetic particles from a plasma. While the degradation of the solid material and the subsequent deposition of the ejected material onto vulnerable surfaces are the usual subjects of sputtering studies, plasma science has yet to be combined with sputtering to create new diagnostics devices and systems. Small changes in the design of the plasma discharge device make it possible to create broad plasma beams for rapid scanning or small plasma beams to obtain the distribution of ejected elements with micron resolution. In the high-resolution use, the ion flux is extracted from the gas-discharge plasma and focused by a spherical emission surface to micron sizes onto the target specimen, providing very local sputtering and local elemental analysis. We call this “self-focusing”. The radiation from the excited and ionized sputtered atoms is recorded by a spectrometer through a window and fiberglass cable and analyzed with standard software packages used for optical glow discharge spectroscopy. Computer simulations of beam formation were used to verify and optimize the designs to be tested. A prototype was designed, constructed, and used to start experiments of beam formation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1986

Electron-cyclotron maser emission from the sun and stars Variations with plasma temperature and density

Very bright and highly circularly polarized radio bursts from the sun, the planets, flare stars, and close binary stars are attributed to the electron-cyclotron maser instability. The mode and frequency of the dominant radiation from the maser instability is shown to be dependent on the plasma temperature and the ratio omega(p)/Omega(e) of the plasma frequency to the electron-frequency. For the emission from the sun omega(p)/Omega(e) is probably greater than 0.3 and for omega(p)/Omega(e) greater than 0.3 and less than the square root of 2, the emission can be either in the x-mode at the second harmonic or in the 0- and/or z-modes at the fundamental. For higher omega(p)/Omega(e), the emission moves to higher harmonics of Omega(e) with the emission being predominately in the z-mode when omega(p)/Omega(e) is greater than about the square root of 3.

Winglee, R. M.↗
NASA NTRS1985

Effects of a finite plasma temperature on electron-cyclotron maser emission

Auroral kilometric radiation, Jupiter's decametric radio emission, and microwave spike bursts have all been attributed to the semirelativistic maser instability. The effect of a finite plasma temperature on the emission from this instability is investigated. Temperature effects reduce the frequency of the x mode and thereby enable fundamental x-mode radiation to occur at higher omega sub p/Omega sub e (where omega sub p is the plasma frequency and Omega sub e is the electron-cyclotron frequency). When the plasma frequency is sufficiently high to suppress x-mode growth, z-mode growth then dominates. The z-mode radiation is, however, subject to electron-cyclotron damping, and this damping can cause heating of the plasma in the vicinity of the source region. In this case, x-mode radiation can be generated even though initial conditions might favor z-mode growth.

Winglee, R. M.↗
DOE OSTI2020

Plasma temperature measurement with a silicon photomultiplier (SiPM)

The temperature of a nonneutral plasma confined in a Penning–Malmberg trap can be determined by slowly lowering one side of the trap’s electrostatic axial confinement barrier; the temperature is inferred from the rate at which particles escape the trap as a function of the barrier height. In many experiments, the escaping particles are directed toward a microchannel plate, and the resulting amplified charge is collected on a phosphor screen. The screen is used for imaging the plasma but can also be used as a Faraday cup (FC) for a temperature measurement. The sensitivity limit is then set by microphonic noise enhanced by the screen’s high-voltage bias. Alternately, a silicon photomultiplier (SiPM) can be employed to measure the charge via the light emitted from the phosphor screen. This decouples the signal from the microphonic noise and allows the temperature of colder and smaller plasmas to be measured than could be measured previously; this paper focuses on the advantages of a SiPM over a FC.

Hunter, E. D. (ORCID:0000000236242840)↗
DOE OSTI2012

Plasma etch characteristics of aluminum nitride mask layers grown by low-temperature plasma enhanced atomic layer deposition in SF{sub 6} based plasmas

The plasma etch characteristics of aluminum nitride (AlN) deposited by low-temperature, 200 deg. C, plasma enhanced atomic layer deposition (PEALD) was investigated for reactive ion etch (RIE) and inductively coupled plasma-reactive ion etch (ICP-RIE) systems using various mixtures of SF{sub 6} and O{sub 2} under different etch conditions. During RIE, the film exhibits good mask properties with etch rates below 10r nm/min. For ICP-RIE processes, the film exhibits exceptionally low etch rates in the subnanometer region with lower platen power. The AlN film's removal occurred through physical mechanisms; consequently, rf power and chamber pressure were the most significant parameters in PEALD AlN film removal because the film was inert to the SF{sub x}{sup +} and O{sup +} chemistries. The etch experiments showed the film to be a resilient masking material. This makes it an attractive candidate for use as an etch mask in demanding SF{sub 6} based plasma etch applications, such as through-wafer etching, or when oxide films are not suitable.

36 MATERIALS SCIENCE↗